In recent years, a rotation angle detector is developed and disclosed. For example, a rotation angle detector for detecting a rotation angle based on a detected angle of rotation of a magnetic field is disclosed in transactions of ‘Transducers 93’ The 7th International Conference on Solid-State Sensors and Actuators, p.p.892 to 895, and in Japanese Patent Document JP-A-H4-302406.
FIGS. 13A and 13B show illustrations of a rotation angle detector 90 disclosed in the above Japanese Patent Document. FIG. 13A is a top view of the rotation angle detector 90, and FIG. 13B is a cross-sectional view of the detector 90 along a XIIIB-XIIIB line in FIG. 13A.
The rotation angle detector 90 shown in FIGS. 13A and 13B has a semiconductor substrate 1 having a trench 1t disposed thereon with two hall elements (Hall elements) on slopes of the trench it for detecting the magnetic field. More practically, the rotation angle detector 90 is made from a p-type silicon substrate 1 with {100} crystal face orientation having a wet-etched essentially square trench 1t which has depth of approximately 100 μm. Each of the two opposite slopes in the trench 1t having {111} crystal face orientation has a hall plate, that is, a low concentration n-type impurity diffusion portion 2a/2b. In other words, the two hall elements in the rotation angle detector 90 have hall plate portions disposed in parallel with the slopes of the trench 1t. Therefore, carriers in the hall plates flow in parallel with the slopes of the hall elements.
The rotation angle detector 90 has a high concentration n-type impurity diffusion portion 4 as wiring for the hall elements 2a, 2b. Reference numeral 3p in FIG. 13B indicates a polysilicon film used as a gate electrode when the low concentration impurity diffusion portions 2a and 2b in the hall elements serve as transistors. The polysilicon film 3p is omitted in FIG. 13A for clarity of representation. Wiring for gate electrodes Ga and Gb are shown in FIG. 13A.
The rotation angle detector 90 having the hall elements 2a and 2b disposed on the opposite slopes picks up magnetic field components Ba and Bb respectively normal to surfaces of the slopes in the trench 1t by using the hall elements 2a and 2b when a magnetic field Bo contained in the XIIIB-XIIIB cross section plane is applied to the detector 90. As a result, induced bias currents la (ai-ei) and lb (ai-bee) respectively proportional to the magnetic field components Ba and Bb in the hall elements 2a and 2b are detected as hall voltages Va and Vb. The hall voltages Va and Vb having different phases are processed in a calculation operation such as an arctangent operation or the like for detecting rotation of the magnetic field Bo in the XIIIB-XIIIB cross section plane.
The rotation angle detector 90 as shown in FIGS. 13A and 13B can detect rotation of the magnetic field Bo in a range of 360 degrees. However, the difference of the phases between the hall voltages Va and Vb makes it necessary to use a complicated calculation operation such as the arctangent operation or the like. Therefore, an operation circuit for processing those operations increases both cost and size of the circuit used in the rotation angle detector 90. The size of the operation circuit becomes larger when the circuit has to detect an accurate angle of rotation for a high speed rotation of the magnetic field. The increase in size of the operation circuit leads to an increased cost of production.